The method in particular includes dropping a plurality of probes intended to partially penetrate into a ground in a predetermined dropping area, to carry out measurements in the ground and/or generating a geophysical stimulus, in particular a seismic signal in the ground with a plurality of sources, each located in a predetermined shooting area.
Each probe is in particular intended to form a receiver including seismic sensors to conduct a geophysical survey in a region of interest.
The region of interest is notably a region with a difficult access. The region in particular comprises a high density of vegetation, such as a forest, in particular a tropical forest. Also, the region may comprise rugged terrain such as hills (for example foothills), cliffs and/or mountains. Also, the region may comprise dangerous to access areas, such as areas with unexploded ordinances (UXO's).
The method can also be applied to any region of interest.
Geophysical measurements obtained during such a survey are critical in building a sub-surface earth image representative of the particular geology in the region of interest, in particular to determine the location of potential reservoirs of oil and gas.
Such a geophysical survey is for example conducted by placing an array of seismic sources on or into the ground in the region of interest and by deploying seismic sensors able to record reflections of seismic signals produced by the successive sources on the different layers of the earth.
The survey generally requires implanting the sources at various locations, and partially introducing receivers in the ground, for instance along several lines or random pattern, to create a dense array of receivers.
The quality of the image obtained after the survey is generally a function of the surface density of sources and/or of receivers. In particular, a significant number of receivers have to be put in place in the ground to obtain an image of good quality. This is in particular the case when a three-dimensional image is required.
Placing sources and sensors in a remote region of interest may be a tedious, dangerous and expensive process. In particular, when the region is barely accessible, such as in a tropical forest and/or in a region with uneven terrain and/or in a region with UXOs, the sources and the sensors must be carried at least partially by foot by teams of operators. In many cases, clearings must be opened in the forest to place on the ground the relevant equipment and operators. Trails must then be cleared in the forest to put in place the receivers.
These tasks create a strong environmental impact in the region of interest and significant health and safety risks for the operators.
The set-up of the receivers and/or the sources in the ground is an extensive process which sometimes requires drilling the ground, and in the case of the receivers, ensuring that the coupling between the receiver and the ground is adequate.
In order to partially overcome this problem, US2015/0053480 discloses a method in which probes are carried by a flying vehicle such as an unmanned aerial vehicle. The flying vehicle is flown above the location at which the probe should be implanted in a dropping area. Then, the probe is dropped from the flying vehicle and falls to the ground.
The acceleration reached by the probe when it impacts the ground provides sufficient energy to at least partially penetrate the ground and provide coupling with the soil for subsequent measurements.
Nevertheless, such a solution is not entirely satisfactory. Indeed, dropping the probes causes severe hazards to the humans and/or animals and/or civil facilities which circulate in the region of interest. If the probe falls on a human and/or an animal, it can cause at best, a severe injury and at worse, a lethal injury. The fall of a probe on civil facilities can also lead to serious material damages.
The same problem arises during the carrying out of the ground survey when sources are used to generate a seismic stimulus. The sources often comprise explosives. Human and/or animal should be prevented from entering the shooting area around the sources.
One solution to try to overcome this problem would be providing a fence around the region of interest to prevent intrusion of humans and/or animals. This solution requires extensive work and materials, especially around regions of large surface area. Moreover, it would require logging large volumes of vegetation to place the fence. This solution would also disturb natural fauna. Additionally, placing a fence around the region of interest is not entirely reliable, as holes may exist in the fence.